import 'dart:io';

Future<void> main(List<String> args) async {
  int res1 = await yuyuyu();
  print(res1);

  int res2 = await yuyuyu();
  print(res2);

  int res3 = await yuyuyu();
  print(res3);
}

Future yuyuyu() {
  return Future(() {
    print('开始执行');
    sleep(Duration(seconds: 3));
    print('结束执行');
    return 123;
  });
}
